In spinal surgery, implant screws or “pedicle screws” are often utilized to stabilize the spine. Typically, these pedicle screws are driven through the pedicles and connected adjacently by rods to manipulate and stabilize the spine during fusion between the bony segments of the spine. Pedicles are two cylindrical or ovoid bones that extend posteriorly from the dorsal surface of the vertebral bodies. Placing these implant screws is typically referred to as “lumbar pedicle screw fixation.” Conventional technique for lumbar pedicle screw fixation involves an open exposure and expanded muscle dissection in order for the surgeon to have a clear and unobstructed access to the spine.
During a back surgery that targets these lumbar pedicles, the entry point into the back is open and exposed. This exposure may lead to extensive blood loss, muscle disruption, post-operative morbidity, lengthy hospital stays, recovery and/or significant costs. In response to this, spinal surgeons and industry have developed minimally invasive surgical (MIS) techniques and technologies, such as posterior fixation delivery devices that enable percutaneous (i.e., “effected or performed through the skin”) placement of pedicle screws and rods.
MIS spine techniques do offer significant benefits over traditional spinal approaches. These benefits include reduction in the blood loss, smaller incisions, muscle sparring approaches, shorter hospital stays, and similar to less complications in well experienced institutions. However, MIS techniques also reduce the visibility of the surgical field and thus make it more difficult for the surgeon to directly visualize the anatomy.
Consequently, when using MIS techniques, surgeons often rely on live fluoroscopic guidance or other equivalent surgical navigation tools. With fluoroscopic X-ray guidance, a surgeon can see the internal structure of opaque objects (such as the living body) by means of the shadow cast by the object examined upon a fluorescent screen when placed between the screen and a source of X-rays. In modern surgery, it's the use of an intraoperative fluoroscope, commonly referred to as a C-arm for real-time x-ray image updates.
Dependence on fluoroscopic guidance for MIS techniques may lead to increased fluoroscopic times. This means that the patients, the surgeon (especially his-hands, and OR staff are exposed to increased levels of X-ray radiation). Moreover, in order to produce these two-dimensional or even three-dimensional views of the anatomy in single or multiple planes, “snapshots” or control shots may be frequently used. Doing this also increases the X-ray-exposure time. In addition, there are other ergonomic challenges with a “C-arm” (fluoroscopic guidance) and these challenges increase the X-ray exposure and risks of contamination to the sterile field.
To enhance and enable these least invasive approaches while minimizing the radiation and sterilization exposure risks, “virtual fluoroscopy” technology can often be employed. Virtual fluoroscopy technology uses calibration and tracking sensor devices that attach to both the C-arm and the patient. The surgeon then prepares to perform a lumbar pedicle screw fusion for target regions of the spine. To prepare for navigation, first a reference “sensor” device is attached to the spinous process via a bone pin or clamp. This is performed through an existing or additional small incision in the back for MIS procedures. The incision in open procedures must be spread wide enough for the surgeon to see, guide, and place both the reference sensor and the implant screws into the pedicles. For MIS pedicle screw procedures, the incision is small and requires x-ray targeting to the spine, but when surgical navigation is deployed, incremental fluoroscopic updates are significantly reduced.
A transmitter is connected to the previously attached reference bone pin or clamp and the surgeon takes and saves to the computer typically two or more different fluoroscopic X-ray views. The calibration device and navigation computer automatically registers the images to the patient's anatomy. During the MIS procedure, the surgeon is able to use these saved and calibrated images to plan trajectories, locate difficult anatomy, and determine other surgical parameters in near real-time using virtual instruments superimposed over the previously saved images, with out the need for continuous updated fluoroscopic shots. In addition to improved accuracy in multi-view tracking, one key benefit of virtual fluoroscopy is reduced x-radiation dose for the patient and the surgical team, since the need for continuous fluoroscopy is eliminated.
Conventional approaches to lumbar pedicle screw fixation often require a significant incision and spreading of the open tissue for the surgeon to see the exposed spine and effectively implant the pedicle screw into the spine. In contrast, less invasive percutaneous approaches for MIS requires small key-hole like incisions through the tissue. The rough or sharp edges of the exposed portions of the specific reference pin or screw for the reference transmitter (sensor), can be difficult to place to the target bone by poor direct visualization and may injure this surrounding subcutaneous tissue during placement. In the end, after the surgery, additional injury may be possible to the surrounding tissue by the removal of the fixated reference screw or pin used to hold the reference transmitter (sensor). It is desirable to make these aspects of a nominally minimally invasive technique to be even less invasive. The patient benefits from doing so are by further reduction in the blood loss, tissue trauma, placement and removal times, medication, quicker discharge, and reduced complications.